The first part of the track from the highway is basically a gravel road and managable on any decent touring bike, but as soon as you descend from the "Scarp" things get extremely difficult. From that point the track is deep, soft sand and you will not be able to ride it on anything other than a fat bike or at the very least a plus bike.
If you call up a few days in advance, you can arrange a pickup at the Scarp from Observatory volunteers, but when we tried to visit the current volunteers were very lazy and would only pick up on certain days (usually it is twice daily). Your luck might be different as the volunteers rotate every six months, so you may have someone nice who is willing to come get you.
Do not undertake this track by bike unless you are well prepared. If you do not have a fat tyres, expect to be pushing your bike through soft sand for about 15km. The attached pictures do not do justice to how soft it is.